The present invention is generally directed to screening of genes or modulators, and more particularly to a transgenic screen for screening biological and chemical test substances for their ability to influence or modulate the production of BDNF in cells.
Brain-derived neurotrophic factor (BDNF) belongs to a group of nerve growth factors called neurotrophins (NT). The function of NTs includes fostering the growth and survival of neurons during development. In adult brains, NTs have an influence on neuronal excitability and, specifically, BDNF appears to regulate neuronal morphology and synaptogenesis. It is also known to exhibit neuroprotective effects in a range of central nervous system areas (Binder et al. 2001). BDNF has been shown to enhance motor neuron survival in several experimental animal models (Department of Neurology, Baylor College of Medicine 2001). Neurodegenerative diseases, such as Huntington's Disease, Parkinson's Disease and Alzheimer's Disease are expected to show abnormal BDNF expression. Enhancement of BDNF function is thought to be one of the mechanisms by which anti-depressants work (Russo-Neustadt et al. 2001) and, as such, might have a significant effect in treating depression.
It is believed that raising the level of BDNF production in the cells would be an effective method of treating various neurodegenerative disease conditions. The current screens for substances that modulate BDNF production are based on cell culturing. Therefore, the screens measure the level of BDNF that is secreted into the culture media and measure changes to this level caused by modulators. However, the screens do not measure the change that the modulating substances effect at the transcription level, and may therefore not be as specific in identifying the action of a modulator.
Other work has also linked the BDNF gene promoter to a fluorescent reporter gene that allows screening for agents which affect the reporter gene expression by affecting the BDNF promoter. One such method was in vitro, involving the culture of a transgenic cell line.
A second existing method involves transgenic mice expressing BDNF promoters linked to a reporter gene. Once again, these mice are able to give a readout on substances that modulate gene expression by affecting the BDNF promoter. However, the mice need to be sacrificed to measure the effect of the modulator, or at least a cell culture must be taken. In either case, the advantages of multiple series of dynamic screens on the same test stock are lost.
The conventional screens, methods, or in vitro tests measure BDNF production directly and do not identify the specific transcription mechanism by which production is increased. BDNF expression is the result of a complex process, however, with a number of regulatory (“promoter” or “cis-”) genes regulating the transcription of the neurotrophic factor. The present invention allows screening for the expression of specific genetic segments, to allow researchers to identify factors that affect the activity of specific promoter genes.